Image intensification tube system



N. scLAR 3,100,845

IMAGE INTENSIFICATION TUBE: SYSTEM Y Aug. 13, `1963 Filed June 1o, 19Go 3d f safrawwf/vesten! ayer 24 67055 /fe irme/ape 607/0216197@ can IN VEN TOR.

NATHAN SCLAR BY KM@ #a5-u.

-JZM ATTORNEYS United States APatent 3,100,845 IMAGE INTENSIFICATIN TUBE SYSTEM Nathan Sclar, Glen Rock, NJ., assigner, by mesne assignments, to Fairchild Camera and Instrument Corporation, a corporation of Delaware Filed June 10, 1960, Ser. No. 35,253 2 Claims. (Cl. Z50- 213) This invention relates to image intensification, and more particularly to image intensiiiers in which electron images are converted into visible images In image tubes which have been used heretofore, the viewing surface, such as the screen of a cathode ray or a television tube, is normally provided with a phosphor coating. When electrons impinge on this coating, a visible image is produced. However, the resultant images in many cases are less intense or less bright than might be desired.

Accordingly, a principal object of the present invention is :to increase the intensity or brightness of visible images which are derived from electron images.

This object is secured in accordance with the present invention by the substitution of a complex including several layers for the conventional phosphor screen.`

One of the layers is of electro-luminescent material. Adjacent the electro-luminescent layer on the side facing theincident electrons is a layer of E.B.C. material. The letters E.B.C. stand for Electron Bombardmentinduced Conductivity. Materials of `this type are normally insulating and become conductive when they are bombarded with electrons. age is focused on the E.B.C. ele-ment, a voltage applied across the two layers is transferred tothe electro-luminescent phosphor. This produces a light pattern in the electro-luminescent` layer corresponding to the electron image. This pattern is many times brighter than the pattern which would appear if a conventional phosphor coating were employed. i

In accordance with a feature of the invention, therefore, an electron tube is provided with a multi-layer coating, including an electro-luminescent layer and an adjacent E.B.C. layer. Arrangements lare also provided for applying a voltage across the two layers, and for applying an electron image to the E.B.C. layer. In accordance with another feature of the invention, image storage and additional intensification may be obtained by utilizing an E.B.C. layer which is also photoconductive Other objects, features, and advantages of the invention will become apparent from a consideration of the following detailed description, and from the accompanying drawing, in which:

'FIGURE 1 is a schematic drawing of an image tube provided with an image intensifier in accordance with present invention; and

FGURE 2 represents the layers at the output of the tube of FIGURE l, and certain associated electrical circuits shown in block diagram form.

`ln `FIGURE l, the tube includes the inner photo-emissive cathode surface 12. Rays of light or infrared energy are incident upon the cathode 12, as indicated by the arrows :14 yin FIGURE l. Electrons corresponding to the incident image are emitted from the cathode 12 within the tube.

.A series of electrodes 16, 18, and are arranged to form an electrostatic electron lens. The electrodes 16, 18, and 20 are biased to appropriate D.C. voltage levels. The general nature of the electron tube of FIG- URE 1 up to this point in the discussion is well known and is described, for example, in an article entitled Image Converters and `Image lntensiers for Military `and Scientific Use, by Myron W. Klein, on pages 904 through 909 of the May 1959 issue of the Proceedings of the Thus,.wheny an electron irnp 3-,l00,845 Patented Aug, 13, 1 963 f. ICC

2 IRE, Volume 47, No. 5. This article is of particular interest for the extensive background of cited yarticles which is included.

Following acceleration by the electron lens system 16, 18, and 20, high energy electrons are focused upon the composite output layer 22 which is within the glass surface 214 at the viewing end of the image intensification tube.

As shown in detail in FIGURE 2, the composite layer 22 on the inner surface of the glass plate 24, includes a thin conducting film 26; a layer of E.B.C. material 28, an electro-luminescent layer 30, and a transparent conducting coating 32, in that order; thus, the two conductive layers 26 and 32 include between them the E.B.C. layer 28 and the electro-luminescent layer 30, and the ent-ire complex is mounted on the glass plate 24 which forms a portion of the tube envelope. Y

An lalternating current voltage supply 34 .is connected to the two conducting layers 26 and 32. 'lhe supply voltage `34 may, for example, have a frequency of 1,000 cycles per second at a voltage of 500 volts. rlhe interrupter 36 is provided to break the circuit from voltage source 34 to layers 26 and 32 by means of suitable `electronic or mechanical switching arrangements 38. The interrupter 36 is not needed in all cases, `and will only be employed when it is desired .to control image storage phenomenon.

In operation, the incident electron image from the cathode 12 is focused on the composite layer 22, as indicated by the arrows 40 in FIGURE 2. When the high energy electrons strike the E.B.C. layer 28, localized areas of the E.B.C. layer become conductive and serve to apply the voltage gfrom source 34 directly across the electro-luminescent layer. The `localized energization of the electro-luminescent layer .30 produces light emission corresponding to the incident electron image. However, the light image is. intensified in comparison with the light output produced by a simple phosphor screenn by a large factor, the additional power for the amplification being supplied from source 34. Accordingly, the image which t is visible from the outside of the glass plate 24 is much brighter than would be obtained with a conventional image tube. Y

With regard to the materials lwhich may be used, the conducting film 26 is preferably` of aluminum, and thin conducting films of other materials may be used. The E.B.C. layer may be of any of a group of known electronic bombardment-induced conductivity materials, such as selenium, antimony sulfide, cadmium sulfide, or cadmium zinc sulfide. For the electro-luminescent layer, Zinc sulfide or other suitable efficient electro-luminescent materials may be employed. VThe transparent conducting coating is preferably of Nesa which refers to a ti-n oxide layer baked into the glass.

With regard to the foregoing materials, reference is also made lto various articles on E.B.C. and electroluminescent materials. Concening E.B.C. materials, the following references are pertinent:

W. Ehrenfest, Chi-shi Lang and R. West, Proc. Phys. Soc.,

volume 64, page 424, 1951;

Kenechi Takeya and Keiichi Nakamura, I. Phys. Soc.

Japan, volume 2, page 223, 1958;

R. W. Decker and R. I. Schneeberger, LRE. National Convention Recond, Part 3, page 156, 1957.

In connection with electro-luminescent materials, reference is made to Electroluminescence and Related Topics, by G. Destreau and H. F. Ivey, Proceedings of the Institute of Radio Engineers, volume 43, page 1911, 1955.

The layers 26, 28, 30 and 32 should normally be quite thin, for example, of the .onder of 0.001 inch, but

tro-luminescent layer presents an impedance which is principally capacitive in nature, the required relative thicknesses of the two layers may be readily calculated for any :given material and frequency of the source 34.

Surrounding the composite layer of image intensification coatings, suitable insulating material or space is provided in the vicinity of the electrode Ztl. This permits energization tof the conducting layers Vfrom source 34 without interference with the D.C. potential applied to electrode 20.

In accordance with the present invention, image storage may be provided for increasing the sensitivity of the device for faint stationary images. The increase in sensitivity may be achieved by integrating the level of the image by` a storage effect until the brightness is adequate for viewing. Inl the case of changing patterns, some blurring and lack :of resolution may occur. To achieveV image storage, optical feedback may be provided by Va suitable choice of materials. Thus, by choosing an E.B.C. material which exhibits photo-conductivity, as well as electron bombardment-induced conductivity, the light emitted by the electro-luminescent phosphor will be in VVpart fed back to cause photo-conductivity in the insulator. The photo-conductive letect VWill then reinforce the E.B.C. effect and provide storage of the image on the electroluminescent phosphor even after the electron beam ceases., With regard to suitable materials, known materials having both E.B.C. and photo-conductivity proper'ti-es include cadmium sulfide and cadmium zinc sulfide.

, Tol clear the stored image from the tube, the voltage from the source 34 may be interrupted by the switching arrangements 38. When very dim stationary images are viewed, a relatively low rate of interruption is desired; with increasing brightness and slow movement, interruption at a-hilgher rateis possible. Accordingly, the rate orf interruption provided by circuit 36 may be varied to archieve the desired optical image. Intennuption at a rate above the optical dicker-perception rate of about thinty toV `fifty yframes per minute is particularly contemplated, as significant additional image intens-iiication may be obtained even at these interruption rates.

It is to be understood that the above described arrangements are illustrative of the application of the principles of the invention. Numerous other'arrangements may be -devised by those skilled in the art Without departing 4from the spirit and scope of the invention.

What is claimed is:

1. A system for intensifying an image of incident radiation including in combination photo-emissive means responsive to said incident radiation for producing electrons, an assembly comprising a layer of electro-luminescent material and a layer tot electron bombardment conductive material over said layer of electro-luminescent material, means for applying a voltage across said Vassembly and means for accelerating saidfelectrons and lfor directing said electrons `onto the surface of said layer of electron bombard-ment conductive material.

2. A system for intensifying an incident radiation image including Vin combination photo-emissive means responsive to said incident image `for producing electrons, an assembly comprising a layer of electro-luminescent material having Igenerally planar surfaces and a layer of electron bombardment conductive material extending over one of said generally planar surfaces of said electroluminescent material layer, a thin film of conductive material pervious to electrons carried by saidlayer of electron bombardment conductive material and a thin transparent lilm of conductive material on the other surface of said electro-luminescent material` layer, means for applyinlg a voltage across said assembly and means for accelerating-saidA electrons and for directing said electrons onto said electron bombardment conductive material through said conductive lm carried thereby.

References Cited in the ilerof this patent 

1. A SYSTEM FOR INTENSIFYING AN IMAGE OF INCIDENT RADIATION INCLUDING IN COMBINATION PHOTO-EMISSIVE MEANS RESPONSIVE TO SAID INCIDENT RADIATION FOR PRODUCING ELECTRONS, AN ASSEMBLY COMPRISING A LAYER OF ELECTRO-LUMINESCENT MATERIAL AND A LAYER OF ELECTRON BOMBARDMENT CONDUCTIVE MATERIAL OVER SAID LAYER OF ELECTRO-LUMINESCENT MATERIAL, MEANS FOR APPLYING A VOLTAGE ACROSS SAID ASSEMBLY AND MEANS FOR ACCELERATING SAID ELECTRONS AND FOR DIRECTING SAID ELECTRONS ONTO THE SURFACE OF SAID LAYER OF ELECTRON BOMBARDMENT CONDUCTIVE MATERIAL. 